[NLM] 2.6.27.14 breakage when grace period expires

[Frank van Maarseveen <frankvm@frankvm.com>]

I'm sorry to inform you but... it seems that there is a similar problem
in the NLM subsystem as reported previously but this time it is triggered
when the grace time expires after a reboot.

Client and server run 2.6.27.14 + previous fix, NFSv3.

On the client there are three shells running:

	while :; do lck -w /mnt/foo 2; done

The "lck" program is the same as posted before and it obtains an exclusive
write lock then waits 2 seconds in above invocation (there's probably an
"fcntl" command equivalent). After an orderly server reboot + grace time
expiration one of above command loops reports:

	lck: fcntl: No locks available

and all three get stuck. After ^C-ing all "lck" loops the server still
shows an entry in /proc/locks which causes the file to be locked
indefinately. Maybe two loops are sufficient to reproduce the issue or
maybe you need more, I don't know.

Interestingly, during the grace time at least one of the "lck" processes
should have re-obtained the lock but it didn't show up in /proc/locks
on the server.

Interestingly (#2), after removing the file on the server (i.e. no
sillyrename) the now free inode is still locked according to /proc/locks.
Even stopping/starting /etc/init.d/nfs-kernel-server plus "echo
3 >/proc/sys/vm/drop_caches" did not remove the lock (it did re-enter
grace).

-- 
Frank